Ocular toxoplasmosis is an inflammatory eye disease caused by infection with the parasite, Toxoplasma gondii. In the US alone, this condition is estimated to affect over 1.25 million individuals. In otherwise healthy adults, who constitute the largest group affected by ocular toxoplasmosis, permanent visual impairment is a common outcome. Particularly aggressive disease is observed in immunocompromised individuals and congenitally infected children. Antimicrobial treatments may suppress growth of the parasite, but side effects are common, and no drug eradicates encysted parasites from the ocular tissues. The overall objective of this work is to understand the basic mechanisms operating in the human eye during establishment of ocular toxoplasmosis. Although there have considerable advances in the field of T. gondii biology, basic questions relating to the mechanisms of human ocular infection remain unanswered. Importantly, it is not known how T. gondii gains access to the human eye from the blood stream. In addition, it is unclear which cell populations within the human eye are preferentially infected by the parasite. Finally, there is no information regarding the impact of parasite genotype on these events. This project is based on the hypothesis that parasites of different strains interact differently with the ocular cells and tissues. The ability of T. gondii or parasitized monocytes to bind to and migrate across human ocular vascular endothelium will be evaluated using in vitro and ex vivo binding assays, and a transwell migration assay, respectively. Movement of free parasites within fresh human ocular tissue will be investigated, and the susceptibility of different ocular cells to infection will be established using dissociated retinal cultures. Selected T. gondii strains will be compared to determine the influence of parasite genetics on the events that occur in the human eye at the onset of ocular toxoplasmosis. PUBLIC HEALTH RELEVANCE: Ocular toxoplasmosis is a vision-threatening parasitic eye infection that is common in the US. No treatment cures the disease. This work will characterize the events occuring in the eye at the onset of the infection, which is an important first step toward the development of more effective treatments for patients with the condition.